This invention relates generally to semiconductor materials and, more particularly, to doping and superdoping in situ a broad family of Si-based semiconductors such as Ge, SnGe, SiGe, and SiGeSn with As, P, and Sb (Group V element).
It has been known for many years—on theoretical grounds—that the SnGe alloy system and the SiGeSn alloy system should have properties that would be very beneficial in microelectronic and optoelectronic devices. This has stimulated intense experimental efforts to grow such compounds. For many years the resulting material quality has been incompatible with device applications. Recently, however, we successfully synthesized device-quality SnGe alloys directly on Si substrates. See M. Bauer, J. Taraci, J. Tolle A. V. G Chizmeshya, S. Zollner, J. Menendez, D. J. Smith and J. Kouvetakis, Appl. Phys. Lett 81, 2992 (2002); M. R. Bauer, J. Kouvetakis, D. J. Smith and J. Menendez, Solid State Commun. 127, 355 (2003); M. R. Bauer, P. Crozier, A. V. G Chizmeshya and J. D. Smith and J. Kouvetakis Appl. Phys. Lett. 83, 3489 (2003), which are incorporated herein by this reference.
In order to fabricate devices using these materials, however, it is necessary to dope thin films of the materials with donor and acceptor elements, such as B, P, As and Sb. Previously known methods for doping Si-based semiconductors with As or P have significant limitations. Typically n-doping is performed using a molecular source approach or by ion implantation using solid sources of the dopant elements. Ion implantation has advantages such as relatively low processing temperatures and the short processing times. However, it also has some major disadvantages, such as significant substrate damage and composition gradients across the film. For the thermodynamically unstable Sn—Ge lattice the re-growth temperatures, that are required to repair the implantation damage of the crystal, may exceed the temperature stability range of the film, resulting in phase segregation and precipitation of Sn. In addition, with ion implantation there are limits as to how much dopant can be introduced into the structure. Ion implantation methods and conventional CVD of the well known PH3 and AsH3 analogs require severe and often hostile processing conditions and are expected to be incompatible with the properties and stability range of the relatively fragile Ge—Sn lattice. In addition PH3 and AsH3 are highly toxic and in fact can be lethal in relatively small doses.
There is a need, therefore, for a method of incorporating appropriate concentrations of activated atoms into the lattice of the Ge—Sn system and in Ge1-x-ySnxEy (E=P, As, Sb) semiconductors and related Si—Ge—Sn—E and Si—Ge—E analogs. It is an object of the present invention to provide such a method.
It is another object of the present invention to such a method that is practical to implement.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by the instrumentalities and combinations pointed out herein.